1. Field of the Invention
Embodiments of the present invention relate to a seat back frame of a vehicle seat.
2. Description of the Related Art
The vehicle seat has a seat back. A seat back described in Japanese Laid-Open Patent Publication 2008-194289 has a seat back main body adapted to support a back of an occupant, and an extension portion extending from a side of the seat back main body. The seat back main body has a main body frame having high structural strength and it's preferably fixed onto a floor. The extension portion has an extension frame supported on the side of the main body frame in a cantilever-like manner. The extension frame and the main body frame each have a circular pipe, and the extension frame and the main body frame are connected to each other by a connection structure. The connection structure has a steel bracket that connects the circular pipes. The bracket extends behind the circular pipes to contact rear sides of the circular pipes. While the connection structure may be resistant to forces approaching the extension portion from the front, it is vulnerable to forces approaching from the rear.
Therefore, there is a need in the art for a seat back frame that has an extension portion with high structural strength.